hpeldsp: add half-pel functions (currently copies of dsputil).
add fixme to hpeldsp.h
remove unused code from hpeldsp_template.c
Split out common pixel functions from dsputil to bit_depth_template.

Move CALL_2X_PIXELS to bit_depth_template.c.
Disable optimizations which I haven't ported yet.
hack in hpeldsp.h to prevent duplicate definition of op_pixels_func
vp3: use hpeldsp instead of dsputil for half-pel functions.
vp3: embed idct_permutation array directly in VP3DecoderContext.

This makes vp3 independent of DSPContext.
indeo3: use hpeldsp instead of dsputil.
binkvideo: use hpeldsp.
interplayvideo: use hpeldsp.
mimic: use hpeldsp.
svq1: use hpeldsp.
vp56: use hpeldsp.
mpegvideo: use hpeldsp.
snow: use hpeldsp.
svq1enc: use hpeldsp.
hpeldsp: remove header hack after removal of hpel from dsputil.
dsputil: remove hpel functions (moved to hpeldsp).
Move x86 hpel assembly from dsputil to hpeldsp.